Abstract Temporal and spatial variations in methane (CH4) emissions from the littoral zone of a shallow mid-latitude lake, Lake Suwa, were examined using the eddy covariance technique. The observation data were supplemented with dissolved CH4 measurement and incubation experiments of lake sediment and water. This lake had areas with steady bubble CH4 emissions, shaping the spatial variation in CH4 flux with strong spot emissions. In the other areas, CH4 was emitted via diffusion and episodic ebullition. CH4 emissions from this area had a clear seasonal variation, reflecting temperature variations, with a maximum monthly mean emission of 0.39 µ mol m − 2 s − 1 in August. The higher emission in summer was due to higher CH4 production in the sediment and the resulting higher dissolved CH4 concentration in the surface water. The steady bubble CH4 emission was seasonally controlled by the total hydrostatic pressure, with higher emission under lower pressure, suggesting regulation of the amount of bubbles emitted from the lake bottom by pressure. Isotope analysis revealed that this CH4 was produced biologically. This natural gas seepage was estimated to emit 1.9 Mg of CH4 annually. Compared with other eddy covariance studies over inland waters, CH4 emissions from Lake Suwa may be large for the latitude. This may be related to eutrophication, which enhances CH4 production.

中文翻译：

---

具有稳定甲烷气泡排放区的中纬度浅湖沿岸带甲烷排放的时空变化

摘要 使用涡流协方差技术研究了中纬度浅湖诹访湖沿岸地区甲烷 (CH4) 排放的时空变化。观测数据辅以溶解CH4测量和湖泊沉积物和水体的孵化实验。该湖具有稳定的气泡 CH4 排放区域，形成了 CH4 通量的空间变化，具有强烈的点排放。在其他区域，CH4 通过扩散和间歇性沸腾排放。该地区的 CH4 排放具有明显的季节性变化，反映了温度的变化，8 月份的最大月平均排放量为 0.39 µ mol m − 2 s − 1。夏季排放量较高的原因是沉积物中 CH4 产量较高，从而导致地表水中溶解的 CH4 浓度较高。稳定的气泡 CH4 排放受总静水压力的季节性控制，较低压力下较高排放，表明压力调节从湖底排放的气泡数量。同位素分析表明，这种 CH4 是生物产生的。据估计，这种天然气渗漏每年会排放 1.9 毫克 CH4。与内陆水域的其他涡旋协方差研究相比，诹访湖的 CH4 排放可能在纬度上很大。这可能与富营养化有关，富营养化增加了 CH4 的产生。据估计，这种天然气渗漏每年会排放 1.9 毫克 CH4。与内陆水域的其他涡旋协方差研究相比，诹访湖的 CH4 排放可能在纬度上很大。这可能与富营养化有关，富营养化增加了 CH4 的产生。据估计，这种天然气渗漏每年会排放 1.9 毫克 CH4。与内陆水域的其他涡旋协方差研究相比，诹访湖的 CH4 排放可能在纬度上很大。这可能与富营养化有关，富营养化增加了 CH4 的产生。